USB Dedicated Charger Identification Circuit

ABSTRACT

In an embodiment, set forth by way of example and not limitation, a USB dedicated charger identification circuit includes a USB D+ port, a USB D− port, a first circuit conforming to a first identification protocol, a second circuit conforming to a second identification protocol, and logic selectively coupling one of the first circuit and the second circuit to the USB D+ port and the USB D− port. In an alternate embodiment set forth by way of example and not limitation, a method to provide USB charger identification includes providing a first USB charger identification at a USB D+ port and a D− port. Next, it is detected if the first USB charger identification was inappropriate. Then, if the first USB charger identification was inappropriate, a second USB charger identification is provided at the USB D+ port and the D− port.

BACKGROUND

The Universal Serial Bus (“USB”) was designed to provide a serialcommunication channel between computers and peripheral devices. Forexample, USB can connect computer peripherals such as such as mice,keyboards, gamepads, joysticks, scanners, external drives, etc. to acomputer. While USB was designed for personal computers it has becomecommonplace on battery powered computerized devices such as PDAs, musicplayers and cellular telephones which use USB for both datacommunication and to recharge their batteries. The design of USB isstandardized by the USB Implementers Forum (USBIF), an industrystandards body incorporating leading companies from the computer andelectronics industries.

There are several types of USB connectors approved by the USBIF,including those with four contacts (pins or sockets), such as the USB-Aand the USB-B connectors, as well as those with five contacts (pins orsockets), such as the mini/micro-A, mini-micro-B and mini/micro AB. Mostcomputers, including laptop computers, have several USB-A connectors,each of which has a power (V_(BUS)) contact, ground (GND) contact andtwo data line contacts (D+ and D−).

Laptop computers are becoming increasingly popular. In order to preservebattery life, most laptop computers have “inactive” modes where they arenot fully on or fully off, such as “sleep”, “standby” and certain“hibernate” modes. During operation, such computers are considered to bein their “active” state, and their batteries may last for a number ofhours. However, by limiting current draws, the batteries of computers inan “inactive” state can last for days.

With some exceptions, laptop computers can charge compliant USB devicesthat are plugged into a USB port of the computer when the computers arein an active state. In such cases, the laptop computer is considered tobe a “USB host.” The devices that can be charged through the USBinclude, but are not limited to, cellular telephones, music players,PDAs etc., collectively referred to herein as “USB devices.” The abilityto charge USB devices through the same USB port used for the transfer ofdata is very convenient and is becoming increasingly popular.

It should be noted that USB devices that do not conform to acceptedstandards (“non-compliant USB devices”) can always draw current from aUSB connector that has power on its V_(BUS) contact. However, there is astrong and increasing desire for USB devices to be compliant with USBstandards. For example, USBIF rules specify that a USB device (one typeof “compliant USB device”) can only draw current from a computer whenthe computer is in an active mode and gives its permission. For example,some laptops will not allow charging through a USB connector if it isrunning solely on battery power. This means that if a laptop computer isin an inactive mode the USB device cannot be charged through thelaptop's USB connector because it cannot communicate with the compliantUSB device. Instead, the USB device can be charged by a dedicated USBcharger (“dedicated charger”) which is essentially a power adapter withan AC input and a USB connector output. The dedicated charger has anidentification protocol which lets a USB device know that it isconnected to dedicated charger.

There are several dedicated charger identification (“ID”) protocolscurrently being used. One, implemented by Apple Computer, Inc. ofCupertino, Calif. (“Apple”), uses resistive voltage dividers coupled tothe D+/D− contacts of the USB connector as illustrated in FIG. 1. Moreparticularly, the circuit inside of an Apple dedicated charger includesa pair of resistive voltage divider circuits, a first of which couplesthe series connection of a 75 K′Ω resistor and a 49.9 K′Ω resistorbetween a 5.0 volt voltage source and ground, and a second of whichcouples the series connection of a 43.2 K′Ω resistor and 49.9 K′Ωresistor between a 5.0 volt voltage source and ground. The center nodesof the two voltage dividers are coupled to the D+ and D− contacts,respectively, of the USB connector. An Apple iPod® or iPhone® USB device(another type of “compliant USB device”), uses a voltage detector todetect the voltages on the D+ and D− contacts as an identificationprotocol for an Apple dedicated charger.

Another dedicated charger identification protocol is specified by theUSBIF. With this protocol, the D+ and D− contacts are shorted as seen inFIG. 2. There is a circuit inside of a compliant USB device asillustrated in FIG. 3 which can detect the short between the D+ and D−contacts to verify that it is connected to a dedicated charger. Chinahas also adopted this convention on a national basis for USB dedicatedchargers.

There are other proprietary dedicated charger ID protocols. For example,Motorola uses 5 contact micro and mini USB connectors with its cellphones and has its own proprietary protocols for the identification ofdedicated chargers. However, micro and mini USB connectors are nottypically provided on laptop computers.

With the USBIF protocol, the circuit inside the USB device detects whenthe D+ and D− contacts are shorted together. This circuit is illustratedin FIG. 3. When a voltage is detected by the USB device on the USB bus,a voltage is applied to the D+contact and a load is coupled to the D−contact. Using a window comparator and a debounce timer the circuitdetermines whether the voltage on the D+ contact is the same as thevoltage on the D− contact, identifying whether the D+ and D− contactsare shorted together or not. A description of the current USBIF batterycharging specification can be found atwww.usb.org/developers/devclass_docs#approved and entitled “BatteryCharging Specification, Rev. 1.1, Apr. 15, 2009, incorporated herein byreference.

To address the problem of not being able to charge a compliant USBdevice on a computer unless it is in an active mode, FairchildSemiconductor Corporation has proposed a solution as illustrated in FIG.4. Based upon the limited information available, it is believed that theFairchild protocol is triggered by the detection of current on theV_(BUS) contact of a USB-A port. Next, it is believed that the deviceshorts the D+ and D− contacts of the USB-A port to emulate a dedicatedcharger following the USBIF protocol. However, it is believed that ifthe current sensed is less than a predetermined threshold level thedevice determines that the device is an Apple USB device and must resetthe Apple USB device detection circuit by cycling V_(BUS) off and thenback on again. A DPDT switch is thrown to connect voltage dividerresistors to the D+ and D− contacts in conformance with the Applededicated charger protocol. If the current sensed with the voltagedividers is greater than the current sensed without the voltage dividersthe switch will remain set and the Apple USB device will charge.However, if the current sensed with the voltage dividers is not greaterthan the current sensed without the voltage dividers, V_(BUS) is againcycled off and on to reset the USB device's detection circuit and theswitch is again activated to short the D+ and D− contacts. When thecurrent sensed is zero, the switch is opened and control is reset, withV_(BUS) remaining on to charge the USB device.

While the Fairchild proposal attempts to address the problem of chargingApple and USBIF compliant USB devices from a USB port of an inactivecomputer, practical implementation details remain significant. First,the V_(BUS) must be monitored. Second, decisions must be made as tocurrent thresholds. Third, V_(BUS) may have to be repeatedly turned offand on as the device iterates through the different possible modes. Thecircuitry and algorithms of the Fairchild proposal are thereforecomplex.

These and other limitations of the prior art will become apparent tothose of skill in the art upon a reading of the following descriptionsand a study of the several figures of the drawing.

SUMMARY

In an embodiment, set forth by way of example and not limitation, a USBdedicated charger identification circuit includes a USB D+ port, a USBD− port, a first circuit conforming to a first identification protocol,a second circuit conforming to a second identification protocol, andlogic selectively coupling one of the first circuit and the secondcircuit to the USB D+ port and the USB D− port. In one exampleembodiment, the first circuit comprises a pair of voltage dividers whichare coupled together in parallel. In another example embodiment, thesecond circuit is a conductor shorting the USB D+ port and the USB D−port.

In an alternate embodiment set forth by way of example and notlimitation, a method to provide USB charger identification includesproviding a first USB charger identification at a USB D+ port and a D−port of a USB connector. Next, it is detected if the first USB chargeridentification was inappropriate. Next, if the first USB chargeridentification was inappropriate, a second USB charger identification isprovided at the USB D+ port and the D− port.

An advantage of an embodiment as described herein is that a USB port ofa USB host such as a laptop computer can be made to emulate a pluralityof dedicated chargers for USB compliant devices such as cell phones andmusic players.

It is a further advantage of an embodiment disclosed herein that the USBport of a USB host can automatically provide a dedicated chargeridentification according to more than one dedicated chargeridentification protocol.

These and other embodiments, features and advantages will becomeapparent to those of skill in the art upon a reading of the followingdescriptions and a study of the several figures of the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

Several example embodiments will now be described with reference to thedrawings, wherein like components are provided with like referencenumerals. The example embodiments are intended to illustrate, but not tolimit, the invention. The drawings include the following figures:

FIG. 1 is a schematic of a prior art circuit inside of a dedicatedcharger manufactured by Apple Computer, Inc. of Cupertino, Calif.;

FIG. 2 is a diagram illustrating the D+ and D− USB data ports beingshorted in accordance with the prior art USBIF dedicated chargerprotocol;

FIG. 3 is a block diagram illustrating the prior art circuit inside of aUSB compatible device in accordance with the USBIF standard;

FIG. 4 is a block diagram illustrating a method proposed by FairchildSemiconductor International, Inc. for emulating dedicated chargerdevices;

FIG. 5 is a block diagram of an example embodiment of a USB dedicatedcharger identification circuit; and

FIG. 6 is a block diagram of another example embodiment of a USBdedicated charger identification circuit.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIGS. 1-4 were described with reference to the prior art. In FIG. 5, anembodiment of a USB dedicated charger identification circuit 10, setforth by way of example and not limitation, includes a USB D+ port 12, aUSB D− port 14, a first circuit 16 conforming to a first identificationprotocol, and a second circuit 18 conforming to a second identificationprotocol. The USB dedicated charger 10 further includes logic 20 whichis configured to selectively couple one of the first circuit 16 andsecond circuit 18 to the USB D+ port 12 and the USB D− port 14. Alsoshown in FIG. 5 is a USB connector 22 which does not form a part of theUSB dedicated charger identification circuit 10.

The USB connector 22, in this example embodiment, has four contacts. Twoof the contacts, namely V_(BUS) and GND, are for power. The other twocontacts, i.e. the D+contact and the D− contact, are used to carry data.As illustrated in FIG. 5, the D+ contact is coupled to the D+ port 12 ofthe USB dedicated charger identification circuit 10, and the D− contactis coupled to the USB D− port 14.

In the example embodiment of FIG. 5, the first identification protocolhas been selected to be the Apple identification protocol and the secondidentification protocol has been selected to by the USBIF identificationprotocol. In other embodiments, these protocols can be reversed, mixedwith other protocols, or replaced by other protocols. However, animportant feature of the embodiment of FIG. 5 is that it supportsmultiple, i.e. two or more, dedicated charger identification protocols.In this example, if the circuit 10 were provided within a dedicatedcharger, that dedicated charger would be operable, for example, withiPods and iPhones (which uses the Apple identification protocol) andwith Blackberry devices (which uses the USBIF identification protocol).In this example embodiment, the first circuit 16 is essentially the sameas the circuit illustrated in FIG. 1 and the second circuit 18 isessentially the same as the circuit illustrated in FIG. 2.

A non-compliant USB device plugged into USB connector 22 can always drawpower from the V_(BUS). However, a USB compliant device can only drawpower from the V_(BUS) if it detects a proper dedicated chargeridentification or if there is proper communication on the D+ and D− datalines to indicate that the USB host (such as a laptop computer) isactive. The USB dedicated charger identification circuit 10 of FIG. 5 istherefore useful in a number of applications. For example, if thecircuit 10 is provided within a dedicated charger it can become a“universal” charger supporting a number of charger identificationprotocols or it can be integrated into a computer to allow charging ofUSB devices even when the computer is in an inactive mode.

With continuing reference to FIG. 5, first circuit 16 includes a firstvoltage divider 24 having a node 26 and a second voltage divider 28having a node 30. According to the Apple Communication Protocol, thefirst voltage divider is the series connection of a 75 K′Ω resistor anda 49.9 K′Ω resistor and the second voltage divider 28 is the seriesconnection of a 43.2K′Ω resistor and a 49.9 K′Ω resistor. This Appleidentification protocol, which conforms to the circuit shown in FIG. 1,preferably uses 1% precision resistors. However, as will be discussed inmore detail subsequently, it is been found that resistors of lowerprecision levels may also be suitable. The first voltage divider 24 andthe second voltage divider 28 are coupled, in parallel, between a 5.0voltage source, in this example, and ground.

The second circuit 18, in this example, is very simple. It is simply aconductor which operably shorts the D+ and D− nodes in conformance withto the USBIF identification protocol for a dedicated charger asillustrated in FIG. 2.

Logic 20 selectively couples the circuits 16 and 18 to the USB D+ andUSB D− ports. In an embodiment, set forth by way of example and notlimitation, the logic 20 includes an electronic switch 32 and controllogic 34. Electronic switch 32 is illustrated as a double-pulldouble-throw (DPDT) switch with the “throws” being coupled to USB D+ andUSB D− ports 12 and 14, respectively, and the “poles” being coupled tocircuits 16 and 18, respectively. In consequence, when the switch 32 isin a first mode, the first circuit 16 is coupled to the D+ port 12 andD− port 14 and when the switch 32 is in a second mode the circuit 18 iscoupled to the D+ port 12 and to the D− port 14. The design andmanufacture of electronic switches are well known to those of skill inthe art and, as will be appreciated by those of skill in the art, othertypes of switches can be used including, but not limited to, optical,magnetic, and mechanical switches.

The control logic 34 allows for the automatic operation of theelectronic switch 32 via a control line 36. In this example embodiment,the control logic 34 includes a parasitic resistor 38, a comparator 40,a comparator 42, and a bistable multivibrator configured as a latch 44.

The parasitic resistor 38, which in this example is 500 K′Ω, couples thecircuit 18 to ground. The comparator 40, in this example, has a negativeor “−” input which is also coupled to the circuit 18 and a positive or“+” input coupled to a 0.4 volt reference. An output 46 of thecomparator 40 is coupled to the reset or “R” input of the latch 44. Thecomparator 44 has a negative or “−” input coupled to node 30 of thevoltage divider 28 and a positive or “+” input coupled to a 2.0 voltreference. An output 48 of the comparator 42 is coupled to the set or“S” input of the latch 44. The Q output of the latch 44 drives thecontrol line 36.

In this example, the USB dedicated charger ID circuit 10 can provide twoidentification protocols, namely, the Apple Identification Protocol andthe USBIF Identification protocol. When a USB device is connected to USBconnector 22, the circuit 10 is in a default Apple identificationprotocol mode with the circuit 16 coupled to ports 12 and 14 by theswitch 32. This is because USB devices conforming to the Appleidentification protocol are undetectable at the ports 12 and 14.Therefore, if a USB device conforming to the Apple identificationprotocol is initially plugged into the USB connector 22, the circuit 10indicates to the USB device that it is a proper USB dedicated chargerand the USB device will charge through the USB connector.

If, however, when a USBIF compliant USB device, such as a Blackberry®“smart phone”, is coupled to the USB connector 22, the defaultidentification protocol, in this example, in inappropriate. However, inthis embodiment, control logic 34 detects whether a USBIF device iscoupled to USB connector 22 and can switch into a USBIF compliant mode.

With continuing reference to FIG. 5 and with additional reference toFIG. 3, it should be noted that the USBIF circuit in the USB deviceincludes a current sink coupled to the D− contact. Therefore, coupling aUSBIF device to the USB connector 22 will pull node 30 to ground and, inconsequence, ground the “−” input to the comparator 42. Since the “−”input is lower than 2.0 volts, the output on line 48 will be HI (e.g. 5volts) and the latch 44 will be set to provide a Q output of HI or “1”on control line 36. This causes the switch 32 to switch from its firstposition to a second position where the circuit 18 shorts the D+ and D−lines.

Once the circuit of FIG. 3 detects that the USB host is a USBIF protocoldedicated charger circuit it will decouple from the D+ and D− ports.This will cause the comparator 40 to develop an output on line 46 whichresets the latch 44, returning switch 32 to its first or defaultposition.

In FIG. 6, an alternative embodiment of a USB dedicated chargeridentification circuit 50 is set forth by way of example and notlimitation. The circuit 50 may be implemented as an integrated circuit(IC) 52 as will be appreciated by those of skill in the art. The IC 52is coupled to a number of off-chip components in a typical USB hostdevice, such as a laptop computer. Some of these off-chip components mayinclude a dual voltage divider 54, a power supply 56, a USB transceiver58 (such as in a Southbridge chip of a PC) and a USB connector 60.

Circuit 50 has many points of similarity with the previously describedUSB dedicated charger ID circuit 10. Therefore, like components may begiven like reference numbers. In an embodiment, a first circuit 54conforming to a first identification protocol is provided by a customeras an off-chip circuit. The first identification protocol, in thisexample, is an Apple dedicated charger identification protocol. In otheralternate embodiments the first protocol can be a different protocol.The reason why a customer may wish to provide the first circuit off-chipis provide high-precision resistors to fully comply with Applespecifications. That is, high-quality 1% precision resistors, or better,could be used in an off-chip implementation of circuit 54 as illustratedin FIG. 6.

However, it has been discovered that in certain applications the use ofexpensive, high precision resistors such as in first circuit 54 are notrequired. In such circumstances, the circuit 54 can be omitted and theRDP pin of the integrated circuit 52 can be coupled to ground asindicated at 62, causing a comparator 64 to activate an electronicswitch 66. In this example embodiment the switch 66 is a double-poledouble-throw (DPDT) switch which couples internal voltage dividers 24″and 30″ to lines 68 and 70, respectively.

It will therefore be appreciated that a customer may utilize theintegrated circuit 52 with either an external Apple compliant circuit orto use the built-in Apple compliant circuit by grounding the RDPcontact. The advantage of this arrangement is that the internal voltagedividers 24″ and 30″ can use lower-quality, and therefore lessexpensive, resistors which meet the voltage requirements of the Appleprotocols but which may not meet all requirements of the Apple protocol.

The electronic switch 32′, in this non-limiting example, is adouble-pole triple-throw (DP3T) switch. That is, the electronic switch32′ of FIG. 6 has one more throw than the electronic switch 32 discussedpreviously with respect FIG. 5. This extra throw is attached to a USBtransceiver 58 which may be, for example, provided in the Southbridgechip of a computer. The other throws can be attached, for example, tothe circuits 54 and 18′ corresponding to the circuits 16 and 18 of FIG.5.

The control logic 34 of the USB dedicated charger ID circuit 50 isessentially the same as the control logic 34 described with reference toFIG. 5. However, the control line 36′ from the Q output of latch 44′ isnot coupled directly to the electronic switch 32′, but, rather, iscoupled to the switch 32′ via control logic 72. Control logic 72, inthis example, can be programmed by its inputs CB0 and CB1 as indicatedby the table at FIG. 6A. When the inputs CB0 and CB1 are both zero, theUSB dedicated charger identification circuit 50 is in automatic or“auto” mode and the signal on control line 36′ is coupled to controlline 36″. Alternatively, the control logic 72 can force a short by, forexample, applying a “0 1” to the CB0 and CB1 lines, force a “resistor”(e.g. force a connection to the Apple compliant charger identificationresistors) by applying a “1 0” to the CB0 and CB1 lines, and couplingthe USB transceiver 58 to the D+ and D− contacts of the USB connector 60by providing a “1 1” at the CB0 and CB1 lines.

It will therefore be appreciated that the chip 52 can be used in adedicated charger but, in addition, can be used in a USB host such as alaptop computer. When used in a USB host, the control logic 72 can beprogrammed by the device by, for example, a pull-down menu. When the USBdevice is active, the USB transceiver takes care of all protocolcompliance with respect to USB devices coupled to the USB connector 60and allows them to be charged through the connector. However, should theUSB host go into an inactive mode, the control logic 72 switched intoits “auto” mode, in which case the circuit 50 operates, in this example,in a matter as described above.

Although various embodiments have been described using specific termsand devices, such description is for illustrative purposes only. Thewords used are words of description rather than of limitation. It is tobe understood that changes and variations may be made by those ofordinary skill in the art without departing from the spirit or the scopeof various inventions supported by the written disclosure and thedrawings. In addition, it should be understood that aspects of variousother embodiments may be interchanged either in whole or in part. It istherefore intended that the claims be interpreted in accordance with thetrue spirit and scope of the invention without limitation or estoppel.

1. A USB dedicated charger identification circuit comprising: a USB D+port; a USB D− port; a first circuit conforming to a firstidentification protocol; a second circuit conforming to a secondidentification protocol; and logic selectively coupling one of saidfirst circuit and said second circuit to said USB D+ port and said USBD− port.
 2. A USB dedicated charger identification circuit as recited inclaim 1 wherein said first circuit comprises a voltage divider.
 3. A USBdedicated charger identification circuit as recited in claim 2 whereinsaid voltage divider is a first voltage divider, and wherein said firstcircuit further comprises a second voltage divider coupled in parallelwith said first voltage divider.
 4. A USB dedicated chargeridentification circuit as recited in claim 3 wherein said second circuitis a conductor.
 5. A USB dedicated charger identification circuit asrecited in claim 4 wherein said logic couples said first circuit to saidUSB D+ port and said USB D− port as a default condition.
 6. A USBdedicated charger identification circuit as recited in claim 5 whereinsaid logic includes an electronic switch having at least two poles withat least two throws per pole.
 7. A USB dedicated charger identificationcircuit as recited in claim 6 wherein said electronic switch couplessaid first circuit and said second circuit to said USB D+ port and saidUSB D− port.
 8. A USB dedicated charger identification circuit asrecited in claim 7 wherein said logic further comprises circuitry havingan input coupled to at least one of said USB D+ port and said USB D−port and an output coupled to said electronic switch.
 9. A USB dedicatedcharger identification circuit as recited in claim 8 wherein said outputof said circuitry is connected to a control input of said electronicswitch.
 10. A USB dedicated charger identification circuit as recited inclaim 8 wherein said output of said control circuitry is coupled to acontrol input of said electronic switch by control logic which controlsan operational mode.
 11. A USB dedicated charger identification circuitas recited in claim 8 wherein said logic comprises a bistablemultivibrator.
 12. A method to provide USB charger identificationcomprising: providing a first USB charger identification at a USB D+port and a USB D− port; detecting if said first USB chargeridentification was inappropriate; and providing a second USB chargeridentification at said USB D+ port and said USB D− port if said firstUSB charger identification was inappropriate.
 13. A method to provideUSB charger identification as recited in claim 12 wherein said first USBcharger identification is a default identification.
 14. A method toprovide USB charger identification as recited in claim 12 wherein saiddefault identification is for an undetectable protocol at said USB D+port and said USB D− port.
 15. A method to provide USB chargeridentification as recited in claim 14 wherein said undetectable protocolis a charger identification protocol developed by Apple Computer, Inc.16. A method to provide USB charger identification as recited in claim15 wherein said wherein said second USB charger identification is adetectable protocol at said USB D+ port and said USB D− port.
 17. Amethod to provide USB charger identification as recited in claim 16wherein said detectable protocol is a USBIF charger identificationprotocol.
 18. A USB charger identification apparatus comprising: meansfor providing a first USB charger identification at a USB D+ port and aUSB D− port; means for detecting if said first USB chargeridentification was inappropriate; and means for providing a second USBcharger identification at said USB D+ port and said USB D− port if saidfirst USB charger identification was inappropriate.
 19. A USB chargeridentification apparatus as recited in claim 18 wherein said means fordetecting comprises circuitry having an input coupled to at least one ofsaid USB D+ port and said USB D− port and a control output.
 20. A USBcharger identification apparatus as recited in claim 19 wherein saidmeans for providing comprises an electronic switch coupled to saidcontrol output of said circuitry.